The time dilation shift is expected to give the largest systematic uncertainty in an ion clock. We show that, in a Penning trap, it can be minimized if the ions are prepared in a special spheroid. The results apply directly for one ion species and approximately for sympathetically cooled systems.>
If environmental perturbations are made negligible, the time-dilation shift is expected to give one of the largest systematic uncertainties in a stored ion clock. In general, this shift increases with the number of trapped ions. Fluctuations in the time dilation shift therefore could limit the frequency stability of an ion clock. We show that in a Penning trap, relativistic time dilation can be minimized if the laser-cooled ions are prepared in a special spheroidal state. In addition, a modest stabilization of the spheroid near the minimum-shift configuration fan significantly reduce fluctuations in the time dilation. The results obtained for a single-species ion clock also provide a good approximation for a sympathetically cooled system.>
Optical clocks based on trapped ions can achieve systematic frequency uncertainties below 10${}^{\ensuremath{-}18}$, enabling relativistic geodesy and precise tests of fundamental physics. However, today's single-ion clocks require averaging times of over a week to resolve frequencies at this level, and no multi-ion clock has been implemented, due to difficulties in controlling ion motion. The authors present an ion-trap array that confines up to 100 clock ions with time-dilation shifts in the low-10${}^{\ensuremath{-}19}$ range, and measure the driven motion of individual ions within an ion crystal. These results point to the next generation of ion clocks, and the realization of clock schemes that have languished.
A multi-ion optical clock with 5×10−19 uncertainty
Today's most accurate clocks are based on laser spectroscopy of electronic transitions in single trapped ions and feature fractional frequency uncertainties below 1×10−18. Scaling these systems to multiple, simultaneously interrogated ions reduces measurement times, driving recent advances in multi-ion clocks. However, maintaining state-of-the-art systematic uncertainties while increasing the number of ions remains a central challenge. Here, we report on a multi-ion optical atomic clock with a fractional frequency uncertainty of 5.3×10−19 and up to 10 \Sr ions. Ion-resolved state detection enables minimization of position-dependent shifts, with residual effects suppressed below the 10−20-level. Clock operation with eight to ten ions reduces the measurement time by a factor of 4.8 compared to single-ion operation. A comparison with an established \Yb single-ion clock yields an unperturbed frequency ratio of 0.6926711632159660405(20), with a statistical uncertainty of 0.9×10−18 and a combined uncertainty of 2.9×10−18. These results demonstrate robust multi-ion clock operation with reduced averaging time and state-of-the-art accuracy.